Flexible power transmission couplings have been used for the transmission of rotary energy from one device to another. Power transmission couplings allow both angular and axial misalignment between rotating machinery, such as the driver and the driving end. Previously, diaphragm type couplings have used a central bore in the diaphragm with a female spline which mates with a male spline formed at the end of the interconnecting shaft. An example of a typical prior art spline coupling is shown in FIG. 1.
Splines, and other convoluted cross-sections, in the interconnections between shafts and diaphragm bores, have failed to perform well in highly stressed torque connections. The splines are typically damaged during use as the torque destroys the spline joint, resulting in inconsistencies in the coupling. The spline couplings fail, in part, because of the large number of stress points 6 created in the interconnection between the diaphragm 2 and the shaft 4. During torque transmission, stress is concentrated on these points 6 which inevitably leads to early failure of the coupling. In addition, rather than an even distribution of torque across the entire surface area of the interconnection, torque transmission is limited to sides 8 during clockwise transmission, and sides 9 during counterclockwise transmission. The limited areas of use of the interconnection during torque transmission not only results in concentrated stress areas which lead to early failure, but also limits the amount of potential torque that could be transmitted.
In addition, some spline couplings are welded together adding expense and possible distortion. Alternatively, the couplings are sometimes bolted or are used with retainers--these additional parts, however, add weight and expense to the coupling. To avoid the additional weight, distortion, and expense caused by extra parts, an interference fit between parts, created through the use of temperature changes, is sometimes used. The diaphragm is heated to allow the splined bore to expand. The shaft is cooled with liquid nitrogen to allow the external splined bore to contract. Then the diaphragm is placed on the shaft to create an interference fit between the spline's grooves. Furthermore, disassembly of a splined diaphragm and shaft, regardless of the method used for assembly, often results in at least some deformity along some part of the spline which makes either or both the diaphragm and the shaft inoperable for further use without time consuming repair.
U.S. Pat. No. 4,411,634 to Hammelmann discloses a flexible coupling having molded plastic flexible diaphragms and molded composite spacer shaft. The plastic diaphragm with an internal convoluted bore is heated, the shaft with an external convoluted surface is inserted in the bore, and the diaphragm is allowed to cool to produce a shrink fit connection between the shaft and the two flexible diaphragms. The use of plastic, however, is not satisfactory in many desired applications, and the procedure in Hammelmann could not be replicated with metal parts using the convoluted connection disclosed. Although the Hammelmann reference eliminates the sharp stress points of a conventional spline, the wavy spline of Hammelmann still encompasses a large number of stress areas, i.e., torque transmission is limited to one side or the other of a "nub". In addition, as with conventional spline cross-sections, the convoluted cross-section requires a high degree of inspection before use, will result in a large degree of fretting during use, and results in sometimes irreparable deformities upon disassembly after use.
Thus, there is a need for a coupling design which eliminates stress points and areas while enhancing torque transmission. There is further a need for a coupling design which utilizes its entire surface area of interconnection for torque transmission. There is further a need for a coupling design which is shaped for easy assembly and disassembly. There is further a need for a coupling design which is easy to inspect.